1. Field of the Invention
The present invention relates to ram type blowout preventers which are hydraulically activated to seal about a pipe string of an oil or gas well to confine and control the pressure therein. More particularly the invention relates to replaceable wear inserts which seal about the pipe and which may be replaced when worn, thus saving the ram for further use. Most particularly the invention relates to replaceable wear inserts for use with heavy rubber ram packers.
2. Related Art
There are many styles of ram type blowout preventers available. One style, as illustrated in U.S. Pat. No. 4,825,948 issued to Carnahan comprises a ram body with a remotely replaceable shoe assembly, the sealing surface being integral with the shoe. The patent discloses ram shoes that are remotely removable and replaceable and includes a good background discussion of blowout preventers in general.
Generally in a very common ram a wear insert is placed in a semicircular cutout on the face of a ram front body. The body of such a ram is usually of a heavy rubber material and the wear insert of an elastomeric material such as TEFLON or high molecular weight polyethylene. The wear insert of this common ram is a very simple semi-circular piece of the elastomeric material with the sealing surface and the insertion surface being parallel. The wear insert may be retained within the ram packer by radial fasteners such as screws. The problem with such an arrangement is that if the opposing ram packers seat at different times around the pipe the wear insert in all likelihood will be twisted out of the cutout by the rotating pipe even when the radial fasteners are used. U.S. Pat. No. 4,323,256 discloses a arcuate insert made of a material having reduced friction.
Another type of blowout preventer is illustrated in U.S. Pat. No. 4,541,639 issued to Williams which comprises a ram body with a ram front packing including a backing portion of elastomeric material and a replaceable insert portion also of an elastomeric material. The wear insert is shaped to include lips that fit into matching slots in the recess. The top and bottom surfaces of the backing portion and insert portion are held together by plates. The insert is tightly engaged with the backing portion and may be removed and replaced only by disengaging and removing the packer from the ram apparatus. To remove the insert from the packer one or both plates are removed and the insert slid axially along seating grooves in the packer. The necessary tightness of fit would probably require that the wear insert therein be driven out of the ram packer from the top or bottom.
A similar arrangement is disclosed in U.S. Pat. No. 4,398,729 issued to Bishop, et al. As in the Williams patent, the Bishop, et al, patent also utilizes metal plates to strengthen the backing portion which with securing members projecting from the insets and cooperating receptacles hold the wear insert in place. Additionally the wear insert of U.S. Pat. No. 4,398,729 includes a pair of securing members extending from the sides to prevent rotation. In column 4 at lines 22-27, the patentee notes that the shape of the insert that fits in the detent on the ram packer can have any configuration in addition to the semi-circular shape shown, so long as the detent in the packer corresponds therewith. The specific configurations mentioned are rectangular and multi-sided. The point of the incidental mention of the insert shape was to prevent a narrow construction of the invention to an insert held in place by the projecting securing members, since the shape of the insert was not significant to the invention of the patent. The securing members and the corresponding notches in the ram packer, serve to prevent lateral rotation in and horizontal displacement out of the detent when the packer is drawn back from the pipe string.
Thus this one feature of Bishop et. al. serves the two necessary functions, but arrangement requires that the entire ram packer be removed and disassembled to replace the insert and the incidental disclosure of the insert configuration was of no moment to the invention.
It is an advantage of the present invention that the insert is non rotational and replaceable without the necessity of removing the ram packer from the blowout preventer. It is another advantage of the present invention that configuration of the insert is simple and can easily casts or machined from a solid block of material. It is a further advantage that the present ram insert is absent any projection thereon for axially slideable engagement with a ram packer.